Multichannel frequency-select system

ABSTRACT

A multichannel frequency-select system which allows for operation of a remotely-controlled device, for example a missile, at various frequencies, e.g. radar frequencies. In the missile, there is located a crystal bank capable of generating a set of reference frequencies one at a time, each crystal of which holds a basic oscillator in a standby position. An automatic frequency control (AFC) circuit in the missile provides a two-speed sweepramp voltage for changing the frequency of the basic oscillator by controlling a voltage-sensitive capacitance or varactor, in the tank circuit of the basic oscillator. A channel selector unit based in a missile launcher provides means to select the desired channel of operation in the remotely-controlled device by furnishing the proper mode voltages, which are related to the sweep voltages, in the device at a precise time.

United States Patent Inventor Michael 8 Primary Examiner-Rodney D.Bennett, Jr.

W98! Covilla, Calif- Assistant Examiner- Malcolm F. Hubler [21] Appl- N3, AttorneysJustin P. Dunlavey, Ervin F. Johnston and John [22] FiledJuly 18, 1969 Stan [45] Patented Mar. 9, 1971 [73] Assignee the UnitedStates of America as represented I by the secretary oflhe Navy ABSTRACT:A multichannel frequency-select system which allows for operation of aremotely-controlled device, for ex- [54] MULTICHANNEL FREQUENCY SELECTSYSTEM ample a missile, at various frequencies, e.g. radar frequencies.4 Claims 12 Drawing Figs In the missile, there is located a crystal bankcapable of generating a set of reference frequencies one at a time, each[52] U.S. Cl. 343/5, crystal of which holds a basic oscillator in aStandby position 343/7 An automatic fre uency control (AFC) circuit inthe missile 01 9 2 q [51] lnt.Cl. G 5 /0 provides a two speed Sweeprampvoltage for changing the Field Of Search 343/5, 5 frequency of the basicoscillator by controlling a voltage sensi (AFC)' 7 (Rs), tivecapacitance or varactor, in the tank circuit of the basic oscillator. Achannel selector unit based in a missile launcher [56] References Citedprovides means to select the desired channel of operation in UNITEDSTATES PATENTS the remotely-controlled device by furnishing the propermode 3,159,335 12/1964 G011? (343/ 5} voltages, which are related to thesweep voltages, in the device 3,212,083 10/1965 I-linchman 343/7( RS )Xat a precise time.

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nereaenc: lX-R) LOOP tests I Q nesleuneo XTAL. c To no 38 =9 I :52?convenes II 36 rue. Q A re mac. i clncun' l 66 none I CONTROL (VAIACTOI)II CIRCUIIT 9 I! V I MISSILE I insult: I I 20 LAUNCHER NE I I LAUNCHER Il8- IF AMP. 7 t I AND sec I I4 I I XTAL F IIODE i e CHANNEL LOGIC ISELETOI I|2 emculr I I LAUNCHER CHANNEL SELEO'YOR PATENTEDMAR 9l97|3,569,965

SHEET 1 0F 9 I' l RADAR G: I FREQ. ll STAGE mun.

| Q 62 l U l/ TRANSFER I BUFFER osc. AMPLIFIER \F ll 27 4} 20 BASIC =Dosc.

. (LC OSCJ 64 MISSILE MISSILE I I RECEIVER CHANNEL-SELECT |BAs|c FREQ. I1T IF AMP. LOW IF AMP. eENERATon J RECEIVER 34 LOOP 6O I DESIGNATEDXTAL. Ac To DC av REFERENCE CONVERTER 1? J1 BANK I 36 FREQ AFC z:$ DISC.CIRCUIT WV L3 MODE END- CONTROL (VARACTOR) CIRCUIT 25 9\ --|2V T 40 I sI E ./|F AND DO u s L J. I l l I MISSILE 2O LAUNCHER IF LAUNCHER IF AMP.

AND AGC l4 v F I XTAL. IF MODE cHANN|. LOGIC SELECTOR cmcun LAUNCHERCHANNEL SELECTOR IN VIiN I ()R.

MICHAEL T. BAGLEY BY ERVIN F. JOHNSTON ATTORNEY. JOHN STAN, AGENT.

PATENTEU MAR 91971 MODE REST FREQUENCY 4 MHz NOMINAL FREQUENCY FIG. 4.3

SHEET 3 BF 9 FREQUENCY CONTROL MODE 3 VOLTAGE CHANNEL LOCK MODE 2 f 5 1B W i av I I nus I I APPROX. 2V, SERIES RES.

APPROX. 2-4V PARALLEL RES.

LOCK POINT APPROX. 0.6V

CRYSTAL RESPONSE K FREQUENCY PATENTED M 9m 3569.965

SHEET 8 OF 9 VOLTAGE FREQ.

l4 A l3 IO no e 1 9 0V LC OSC. 6 a 4 TANK-TUNED 5 BY VARACTOR .7 4 6 v?3 5 L 2 4 CH1 3 RC F l G 7 2 TIME EQUIVALENT CONS T CIRCUIT o ar-TmE =1STATED VALUE OF CAPACITY so (VARACTOR) so i a 4 8 l2 I6 20 24 2a 32 asems VOLTAGE l8 MODE SIGNAL LINE COAX FROM MISSILE Low MODE QA IF AMP- sR LOGIC AND AGC XTAL c CIRCUIT l l T:- lG Y '4 I CR7 Rl3 20v 0cREGULATED '0 I le'flf IN SHUNT (RI3BIRI4) 20V DC MODE VOLTAGE cs Q 3VARACTOR A ACTIVE cmcurr AFC CONTROL CIRCUIT MODE 2 FIG. 9.

J 41oo 100,47 4700 inc f magi I 8 EQUIVALENT cuncun' VARACTOR A-ACTIVEcmcun' AFC CONTROL cmcun- MODE 3 j v FIG. IO.

MlJlL'lllCl'lAhlNEl. FREQUENCY-SELECT SYSTEM The invention describedherein may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentof any royalties thereon or therefor.

in the prior art, are multichannel frequency-select systems and thereare systems incorporate a sweep voltage which aids in obtaining thedesired frequency of operation. However, they all have disadvantageswhich will be pointed out in the brief description which follows.

The first system of the prior art to be discussed includes a systemwherein there is a dual output from a discriminator network, each outputbeing similar in shape to a typical FM discriminator output, i onediscriminator output being the mirror image of the other. A key featureof this prior art system is that the local oscillator locks a frequencydetermined by one of the discriminator outputs and not the other.Strictly speaking, this system hardly qualifies as a frequency-selectsystem, inasmuch as the system merely discriminates between two sidebandfrequencies. The second multichannel frequencyselect system to bediscussed solves the difficulties involved with a phase-lock oscillatoroperating at more than one frequency, in that in order to properly lockonto the desired frequency, a sine wave, derived from the output of theoscillator, is sampled preferably at the zero crossing for thatfrequency. However, it is difficult to have sampling at precisely zerocrossing for more than mitigated. frequency. temperaturecompensation cantemperature-compensated temperaturesensitive detrimentally In anothersystem in the prior art, there is a crystal-controlled oscillator whosefrequency may be varied to a limited extent, thereby permitting severaloutput frequencies when passed through various narrow-band filters. Asmay be seen, this system has the disadvantage that the severalselectable frequencies must be close to each other. Another prior artsystem includes a method of precision tracking of electrically tunedcircuits, wherein a control voltage for a reactance element is obtainedfrom a discriminator of an automatic frequency control circuit of anoscillator. if the frequency of the oscillator drifts, the outputvoltage from the discriminator drifts in a direction which would tend tobring the oscillator frequency back to its desired value. The sameincremental DC voltage change is applied to a reactance element in atuned circuit to be controlled, so that the frequencies of the two tunedcircuits are effectively locked together. In addition, there is featureda means varying a basic oscillator frequency, for example by insertingone of several alternate resistors in series with capacitive reactanceelements of the tank circuits. The system herein described is rathercomplex and has the further disadvantage that it includes many sets oftapped switches, which tapping is always subject to corrosion and poorcontacts, thereby causing very noisy circuits. It should be pointed outthat, in all of the prior art just discussed not of it had the featureof controlling an oscillator frequency at a remote location. Theinvention herein disclosed describes a multichannel frequency-selectsystem wherein it is desired to select a frequency at one location, forexample on a missile launcher channel selector with the same channel ata remote location, for example, an oscillator located on a missile.

Following is a brief description of the invention.

inasmuch as the system operates in three different, successive, modesfor the circuitry in both the missile launcher and the missile, with aspecific mode of in the launcher preceding that of the same mode in themissile, the multichannel frequency-select system will be described withparticular emphasis on the modes of operation.

Mode 2 is a preset mode, in which the frequency of oscillation in themissile is a rest frequency.

Mode 2 is a channel" select mode in which the frequency spectrum coveredby the crystal bank in both the missile launcher channel selector andthe missile is swept or scanned at a rapid rate.

Mode 3 is an acquire mode, wherein the scanning rate slows down andstops when lock is acquired.

Modes )1 and 2 may be manual or timer-controlled or work on AGC, missilebattery power, or when the heterodyned signal from a low-frequency IFamplifier is present and detected in a switching device. Mode 3 is:initiated electronically by the sweep scan frequency corresponding to aplotted crystal or band-pass frequency in the launcher channel selectorunit. attenuation network radio be transmitted The manner in which thevarious channels are changed and tracked is a key feature of thisinvention. In the missile, the whole Fl 19 different crystal-controlledfrequencies and the single F2 the shown. selector in the embodimentdisclosed, is scanned, at a rapid rate in Mode 2. ohms. The channelselector in the launcher completes its function when the scanningfrequency corresponds to the channel crystal selected, this in turninitiates Mode 3. The channel selector becomes inactive after Mode 3 isinitiated.

In the missile itself there is a circuit in which the time changes (witha longer time constant in Mode 3), the change in the time constant beingin step with the variation in the frequency scanned in the missilecrystal bank. When the intermediate frequency (IF) in the missile, whichscans upward in frequency, corresponds the desired frequency of thecrystal in the crystal band of the missile, it represents the desiredchan-.

nel, the sweep is stopped and the AFC of the crystal reference loop orthe receiver loop takes over. There may also be a return radar signalreflected off the missile and returned back to the missile launcher,which may assist an automatic frequency control (AFC) circuit equalizerthe missile launcher in locking onto the specific desired frequency. db

' As stated above, there are two ubanks, H; the missile launcher and onein missile. The resonant frequency of a particular in the crystal bankon the missile launcher is lower than the frequency of the correspondingin the crystal bank the missile, thus allowing for sweep time in thelauncher to lock onto the proper crystal *H; H;

The sweep of the frequencies 12 the missile launcher channel selector isin step with the sweep of the frequencies in the missile crystal bank.The sweep of the frequencies originates in the missile and thiscompensating is the same in the missile launcher channel selector. Asignal goes back from the missile to the missile launcher channelselector. The same sweep and IF appears in both, the missile and themissile launcher. When the sweep frequency in the missile launcherchannel selector attains the desired frequency in the channel selectedan SCR transistor fires and initiates Mode 3. The sweep continues at amuch slower rate. Once the desired frequency is acquired, with aspecific crystal frequency chosen from the crystal frequency bank themissile, the sweeping operation ceases. An AFC circuit in the missilelauncher locks the chosen frequency the operating frequency of themissile itself. Circuitry in the missile launcher selector includes anelement which fires and initiates Mode 3. This, in turn, sendsseries-connected Mode 3 (zero voltage) signal back to the missile, whichremoves a voltage in the an and initiates the slow sweep (time constantchange). there were no disabling circuit, lock would be achieved on thefirst crystal. When the El taken off F2 the that is, inactivated, thenext higher frequency in the crystal bank in the missile is the onewhich is locked onto, instantly stopping the sweep. This next higherfrequency is several hundred kilol-lertz kHz. above the correspondingfrequency in the missile launcher channel selector crystal.

After the scanning of the frequency spectrum in the missile launcher hasstopped, at the end of Mode 3, it does not resume scanning for thatmissile operation. In effect, the frequency acquisition is a one-shot"operation. An AFC circuit, having a frequency tolerance, keeps it lockedat the proper frequency at which the particular missile operates. Thereis a multiplicity of channels in order to avoid interference, inoperational use, between various ships in the same general areaattempting to control their respective missiles at the same time. Asystem could have been developed with only one fixed frequency for themissile and a reference crystal band only in the missile launcher,however such a system would not be as versatile or adaptable or asinterference-proof as one with a crystal bank in both the missilelauncher and the missile.

Accordingly, an object of the present invention is the of a multichannelfrequency-select system which permits selection of any one of 19 channelfrequencies. The channel selected has its frequency automaticallycontrolled by the missile receiver loop or the channel guard bandcrystal.

Another object is to provide a multichannel frequencyselect systemwherein any crystal (guard ba'nd crystal) in a reference crystal bank,located on the missile, can employed without individual crystal H;

A further object the invention is the provision of a multichannelfrequency-select system in which either series or parallel crystalresonance can be used.

Still another object is to provide a multichannel frequencyselect systemwherein any channel in the crystal reference bank can be reached withina very short time, less attenuation I msec.

Yet another object of the present invention is the provision of amultichannel frequency-select system using a 2-speed single-ramp wave, afast sweep for channel selection and a much slower sweep in the channelregion prior to locking onto the desired frequency. Other objects andmany of the attendant advantages of this invention will be readily asthe same becomes better understood by reference to the followingdetailed description, when considered in connection with theaccompanying drawings, in which like reference numerals designate likeparts throughout the FIGS. thereof and wherein:

FIG. 1 is a F1 diagram of the complete multichannel frequency-selectsystem, for circuitry on both the missile and the missile launcher. F2detrimentally FIG. 2 is a set of graphs showing:

A. the crystal responses in the missile; B. the manner of frequencyscanning; and and C. the three mode control voltages generated in thelauncher temperature-sensitive conducted to the missile. close-loopopen-loop open-loop voltage-controllable FIG. 3 is a graph showing thevariations in ramp voltages and frequency for the three modes ofoperation.

FIG. 4 is a different diagram showing: voltage-controllable PIN so of A.series; and DC DC B. parallel connection for the crystals in the crystalbanks in the multichannel frequency-select system; and oscillator C. theAFC discriminator response point for both. FIGS. 5A and 5B are primarilyschematic diagrams of the missile channel selector.

FIGS. 6A and 6B are partly block and partly schematic diagrams of themissile crystal-reference X-R (from Xtal Reference) loop.

FIG. 7 is a pair of graphs showing: frequency-selective DC is DC DC F3A. DC voltage on the DC used to control the frequency of the basicfrequency generator as a function of time; and B. the capacitance ofvaractor as a function of the bias voltage on the varactor.

FIG. 8 is a diagram, primarily in block form but partially schematic, ofthe mode DC loop circuit. DC .02uF. DC emitter-base FIG. 9 a schematicdiagram of A. active; and across-the-band B. equivalent circuits of theautomatic frequency control (AFC) circuit of the missile in Mode 2. F3closed-loop FIG. 10 is similar. type forth schematic diagram foroperation in Mode 3. claims. Referring now in more detail to the FIGS.and beginning with FIG. 1, there is shown herein the three basic circuitblocks of the multichannel frequency-select system, namely, amissile-launcher channel-selector 10, a missile crystal-reference loop(X-R loop) 20, and a missile receiver loop 60. A few of the circuitblocks are common to both loops. The components that make up the X-Rloop include the blocks labeled 34, 38, 36, 25, 24, 26, 27, 32 and backto block 34, the totality of the blocks forming a closed circuit loop(AFC loop), or servo loop. In the embodiment shown, transfer oscillatormust be considered part of the X--R loop, along with low IF amplifier32. In a simplified embodiment, discussed hereinbelow, neither of thesecircuits would be necessary.

The components that make up the missile receiver loop 60 include theblocks labeled 66, 36, 25, 24, 26, 28, 63, 64 and back to block 66,these blocks also forming a closed circuit loop (AFC loop) or servoloop. temperature-sensitive The launcher chanr iel selector unit 10provides a means to select the desired channel of operation in themissile by furnishing the proper mode voltages, by means of mode controlcircuit 40, into the missile at a precise time. A single crystal orbandpass device in the launcher channel selector 10, when scanned by thevariable basic oscillator 24, and by means of the low IF amplifier 32triggers the mode logic circuit 14 into Mode 3 (only function), thusactivating the missile receiver loop 60 and the X-R loop 20 and allowinga channel lock onto either loop. If the missile receiver loop 60 has aradar signal, it will lock onto it with the X-R loop 20, providing abarricade or stand-by position in the event of loss of signal in thereceiver loop. The launcher channel selector 10 is remote from themissile in one embodiment actually built, but could be used as part ofthe missile and its functions controlled by a radio link from theground.

The circuitry on the missile launcher channel selector 10 is connectedto circuitry on the missile by a single-wire coaxial cable 19 whichcarries all the information necessary for channel selection, namely: 1.the RF sweep signal; 2. the +12 V DC Mode l voltage; 3. the 12 V DC ordisable voltage, for Mode 2; and the Mode 3 zero V DC or enable voltage.

Discussing now the major circuits in the missile crystal reference loop20, one element of the basic frequency generator 22 includes a basicoscillator 24, which is an LC oscillator that is frequency-controlled bya voltage-sensitive capacitor in its tank circuit, that is, by avaractor 25. The output of the basic oscillator 24 feeds a bufferamplifier 26, which in turn powers a frequency-multiplying system, orfrequency multiplier 28. One output of the buffer amplifier 26 is mixedin mixer 27 with a transfer oscillator 30 to lower the frequency to amore practical value for transmission to the remote location of thelauncher channel selector unit 10. The transfer oscillator 30 is afixed-frequency crystal-controlled oscillator operating at a frequencywhich is approximately 60 MHL, above that of any of the crystals in thecrystal reference bank 34. Mixing of basic oscillator frequency with thefrequency of the transfer oscillator 30 results in an intermediatefrequency (IF) which is equal to the difference between the twofrequencies. This IF is nevertheless an RF frequency.

The crystal reference bank equalizing is a grouping of piezoelectricquartz filter'crystals each of which provides the reference frequency ofthe guard band in the X-R loop 20. The guard band of the desired channelholds the basic oscillator 24 in a standby position for the missilereceiver loop 60 to take over control of the basic oscillator when themissile receiver loop is active. By the very nature of an AFC loop, theloop corrects the oscillator frequency, thereby eliminating the errorsignal. The radiofrequency (RF) output of the reference band 34 isconverted to a DC voltage, by means of DC converter 38, supplying thelock and error signals for the X-R loop 20. 1

An AFC circuit 36 provides a two-speed sweep-ramp, that is, a triangularsweep voltage having two slopes, connected to the varactor 25, which inturn changes the frequency of the basic oscillator 24, to cause a lowerintermediate frequency (IF), which is amplified in low IF amplifier 32.preselected Connected between the crystal reference band 34 and the AFCDC amplifier 36 is an AC to DC converter 38 that stops and locks thesweep, and provides the DC DC AFC amplifier 36 is controlled by themissile receiver loop 60, which preempts control of the basic oscillator24 when the missile receiver loop is active. voltage-controlled thereceiver signal is present, an error signal is introduced, thus againthe frequency is corrected. cable, It should be pointed out that, themissile receiver loop 60 is not needed to lock the selected channelcrystal. In fact, voltage-controlled no signal appears in the missilereceiver IF amplifier 6%, loop ht is open, and system. will lock ontothe guard band crystal (stand-by).

Discussing now the missile IF and RF receiver AFC loop 6t), themultiplied signal from the frequency multiplier 28 is mixed with areceived radar signal from radar stage 62 in the mixing circuit #63,forming an IF signal amplified by the missile receiver lF amplifier 64.When the IF signal is mixed with the radar reference signal, theresulting signal is a band-centered IF signal which is maintained by themissile receivers AFC closed loop oil. The missile receiver IF amplifier645 is terminated in a frequency discriminator 66 that furnishes lockand error signals to the AFC circuit 36 to provide control of the basicoscillator 2t and its frequency-multiplying system, the AFC action thuseliminating the error signal.

Both the X-R loop 20 and the missile receiver loop 60 are automaticfrequency control (AFC) loops. The X-R loop 20 holds the basicoscillator X-R (LC oscillator) 24 within the error limits of the channelselected. When a target signal, a radar signal, is present in themissile receiver loop 60, it preempts control of basic oscillator 24, byintroducing an error signal which pulls the basic oscillator lower infrequency away from the influence of the guard band crystal. One loop orthe other is active: with no target signal, the X-R loop AFC is active;with a target signal, the missile receiver loop 20 is active. Themissile receiver loop 6% is active under the following circumstances.When a homing signal, that is, a target signal, is present in themissile receiver till, the AFC of the receiver controls the basicoscillator 24 thus reducing or eliminating the radar error. If thesignal (target) is interrupted or lost, the crystal-reference loop 20resumes control and holds the basic oscillator 2% within error limitsuntil the receiver signal is restored.

Both the crystal-reference loop 20 and the missile receiver loop as arefrequency discriminators. When the basic oscillator 2,4 is in a standbycondition, the crystal acting as a discriminator presents the necessaryerror signals to control the basic oscillator. A signal in the receiverdiscriminator 6b is a plus error signal which drives the basicoscillator 24 lower in frequency away from the guard band into thereceiver discriminator crossover curve at band center. An error signalbelow this crossover presents a minus error voltage which drives thebasic oscillator 24 higher in frequency. Thus at crossover, correctivevoltage-controlled signals are eliminated. voltage-controlled Beforediscussing the manner of operation in detail, it will be useful to makea few general remarks about the multichannel frequency-select system.

Any crystal in the reference bank 34 can be employed without individualcrystal switching. Series or parallel crystal resonance, as is shown inFIGS. 4(A) and 4(8), respectively, can be used and the response slope,as is shown in FIG. MC), can be used as an AFC discriminator forfrequency error control. A system of disable and enable voltages (seeFIG. 2) generated by the mode logic circuit M are switched by thecrystal channel selector R2 at precise times. This is made possible byscanning the crystal bank 34 of the missile and the crystal channelselector l2 of the launcher channel selector it) simultaneously. Acrystal or other band-pass device in the crystal channel selector l2will switch the disable voltage off the crystal reference bank 3'4 justbefore it approaches the desired crystal, thus allowing it to lock ontothis crystal. This is accomplished because the crystal, or some othertype of bandpass device allows the IF scanning signal to go through tothe SCR, which fires (like a switch) thus cutting off the disablevoltage. This locking is termed guard band lock. If the missile RFreceiver loop 60 is active, it will lock onto it before reaching theguard band. On loss of missile receiver signal, the signal will movehigher in frequency, and it will lock onto the guard band crystal, thisbeing a standby position whereby the missile receiver can always preemptcontrol. The sweep control system receives its commands from the disableand enable voltages (mode voltages) produced by the crystal channelselector unit I2.

Any channel in the crystal reference bank 34 in the missile can bereached in 50 msec. 100 msec. is required for any channel in the crystalchannel selector l2. Either the X-R loop 2ft or the missile receiverloop can exercise control in the AFC circuit 36 of which the sweepcircuit is a part. The sweep circuit furnishes a fast sweep for channelselection. then a very slow sweep in the channel region prior to Thenumber of crystals in the crystal reference bank 3M corresponds to thenumber of channels desired. In the embodi ment disclosed, 19 were used,consisting of 4 groups having 4 in each group and 1 group of 3. regionwhich Two groups of four crystals are shown in FIG. 6A. As may be seenfrom this F IG., in each group, of four or three crystals, the seriescapacity of the crystals is reduced to a small value by shunt chokesL-yl and L-y5 which are tuned to near resonance, and uses separate dioderectifiers CR3 and CRIO with 1.5K resistors R18 and R19 as a DC return.The crystal reference bank 34 is driven by a single signal source, thelow IF amplifier 32, and the output impedance is reduced by 1,500/5 300;this reduces crystal hank feed-through by a factor of 5. Also, the caseof each individual crystal is grounded to reduce feedthrough.

With respect to alternative embodiments, can be readily understood byone skilled in the art that a multichannel frequency-select system couldbe devised not requiring a transfer oscillator 30 nor a IF amplifier 32,but instead feeding the output of the basic frequency generator 22directly into the crystal reference bank 34 and into an amplifieranalogous in function to launcher low IF amplifier 16, but which couldno longer be termed an. IF amplifier. The system herein described hasdistinct advantages over such a simplified system. The manner in whichthe voltage on the varactor 25 is related to frequency is shown i N FIG.2. When a guard band crystal is selected, it presents a stone wall" toany further rise in frequency. In other words, this sets a frequencylimit. It can go lower in frequency ifthe missile receiver loop 60 isactive, to a point of discriminator crossover, or no-error signal.

Inasmuch voltage-controlled the three mode voltages shown in FIG. 2 arevery important in the of the manner in which the multichannelfrequency-select system operates, the description of the operation willbe keyed to the three modes. Reference is directed to FIG. 3, whichshows the voltage at the varactor (25 in FIG. I) and the frequency ofoscillator as a function of the modes.

Mode 1: Missile Launcher In this voltage-controlled the basic oscillator24 in the missile is oscillating at a rest frequency, in one embodimentwas 4 MHZ. The voltage on cable 19 and therefore on the mode signal linelb is-l-l 2 V DC.

On the missile DC channel selector I0, one of the I) voltage-controlledchannels is selected by at single-pole l9-position rotary or pushbuttonswitch, shown as SW-I to SW-I9 in FIG.

7 5A. The preset-select switch is in FIG. 5B is closed, that is,

set to the preset position 15A. This sets up Mode l by permittingcurrent flow through diode CR-Al (W914) and sets up transistor Q-A(2N894) for channel selection signals. Transistor Q-A is asilicon-controlled rectifier (SCR) switching transistor, and under Model conditions is open," or nonconducting Transistor Q-B is also cut offby bias voltage through diode CR-Bl and the closed preset-select switchI5. The closed" preset-select switch E5, in position ISA, puts a 28 V DCpotential through a resistor R1 (47 K) on the base of transistor QC(2N2907A), which saturates this transistor, resulting in maximumconduction. The resulting mode signal voltage at the mode signal line 18is +28 9.1 5 +1 9.0

Mode l: Missile The crystal channel selector 12 is now ready for missilelaunch and therefore'the missile is ready for launch.

In the preset Mode l, with the preset-select switch 15 of FIG. 5B in theselect or open position 153, the following trans pires, beginning withthe application of the +12 V DC Mode 1 voltage (as may be seen in FIG.1). Current flows from the mode logic circuit 14, of the launcherchannel selector 10, through the mode signal line 18, through thecoaxial cable 19, and into the mode control circuit 40, whence it isdistributed to various circuits.

Referring now to FIG. 6A, the +12-volt Mode 1 voltage is distributed asfollows:

a. Through the two resistors R11 and R20 forming a voltage divider toground, through resistor R18, and through diode CR3 and inductance L2.Referring now to FIG. 6B, the +12 V enters the AFC circuit 36 throughthe base of transistor Q1, saturating its collector, whereupon thepotential across condenser C1 drops to a value near zero. Transistor Q1normally conducts with a bias voltage greater than +0.6 V, otherwise itis cut off.

b. Through resistor R2, diode CR5, and into the base of transistor Q3,reducing the potential across condenser C4 to a value near zero. t

c. Through resistor R6 into the base of transistor 05, reducing thepotential across capacitors C6 and C7 to a value near zero, placing thesweep circuit into its ground state.

This corresponds to the rest frequency of the basic oscillator 24, andis shown as Mode 1 in FIG. 3.

Summarizing the +12 V DC Mode 1 voltage saturates transistors 01, Q3 and05 (see FIG. 6B), which in turn effectively shorts out the capacitorswhich make up the capacitance C of the RC sweep circuit. The conditionshown in the circuit of FIG. 7A now exists.

In FIG. 6B, capacitors C1, C2, C4 are used as Miller capacities, and aremagnified by the gain (1 A) of the transistor Q1, Q2 and Q4,respectively, to whose collector they are connected, A being the gain ofthe transistor. Condenser C 1 and transistor Q1, for example, incombination result in the well known Mill er effect, which is a voltagemultiplication of capacitance.

Still referring to FIG. 6B, the capacitance of condenser C10 ismagnified by the beta of transistor Q7. The multiplication of thecapacitance of condenser C10 by transistor O7 is believed to be a novelresult. Capacitance-multiplying by current methods is to be contrastedwith the voltage multiplication of capacitance just discussed. Thefunction of the circuit which includes condenser C10 is to offerresistance to scanned jamming signals and to prevent loss of channel inthe event of jamming. It offers a long time constant so that signals ofshort duration will not take over.

Mode 2: Missile Launcher In Mode 2, the missile power is up, that is,the battery is activated and the missile is made ready for launch. Someof the ways in which power in the missile can be used to automaticallyinitiate Mode 2 in the channel selector 10 is by detection devices, suchas those which sense when the actuated missile battery voltage is up tonormal or the basic oscillator 24 heterodyned signal is present in thecrystal channel selector 12. These are two ways which may be used tostart the sweep in the in starts in Mode 2. In the methods hereindisclosed, as the multichannel frequency-select system was used in thelaboratory and for operational use, it was only necessary to flip thepreset-select switch into the select or open position 153, as shown inFIG. 5B.

In the select Mode, after the preset-select switch 15 is flipped to theselect position 15B, in the launcher channel selector unit 10, within 1msec. or less, the mode voltage switches from +12 to l 2 volts (refer toFIG. 2C), the :12 V resulting from a 7-volt drop across a Zener in themissile. The sweep ramp voltage starts to rise instantly, changing thefrequency of the basic oscillator 24 upward with it, as may be seen inFIG. 3.

The following now takes place in the launcher channel selector 10. Referto FIG. 5B. The preset switch 15 is still open. Transistor Q-C (2N2907A)cuts off, the +l9.0 V DC voltage at resistor R2 drops out. TransistorQ-B (2N2222A) conducts, the --l9.0 V DC cuts in. Transistor Q-A (2N894),which is a switching transistor, remains cut off. Mode signal voltage onmode signal line 18 is now I 9.0 V DC as a result of transistor QBconducting. I

Meanwhile the basic oscillator 24 in the missile starts up from its restfrequency of approximately 4.0 MHZ. (see FIG. 3) and sweeps upward infrequency. When the RF frequency reaches the band-pass or crystalfrequency, it fires the transistor Q-A (2N894), a silicon-controlledrectifier, which immediately decreases the magnitude of the mode voltagefrom 1 2 V DC to zero, at the end of Mode 2, in 0.5 msec. or less. SeeFIG. 2C.

As may be seen in FIGS, the crystal Y-N provides the path between thelow IF amplifier 16 and the Q-A SCR. The SCR fires on RF signal, itsaction being not unlike that of a thyratron.

In the laboratory embodiment, and referring back to FIG. 58, if theoperator wishes to select a different channel before missile launch, thepreset-select switch 15 is returned from the select position 158 to thepreset position 15A, the desired channel is switched in, then the switch15 is returned from the preset position 15A to the select position 153.There is no limit on the number of times this can be done except forconsiderations of battery life of the missile. While the battery life isapproximately 12 min. in the embodiment actually built, only 0.5 min. ofthis represents the. drain on the missile launcher.

Mode 2: Missile The following is what transpires in the missile in Mode2. As stated above, within 1 msec. after the preset-select switch 15 isflipped to the select position 158 (see FIG. 5B), the mode voltagechanges from +1 2.0 to l 20 V (see FIG. 2C).

Within this same time of 1 msec., the l 2 V mode voltage is distributedas follows, referring first to FIG. 6A.

a. through the two resistors R11 and R20 forming a voltage divider. Thisnegative voltage of 12 V puts a reverse bias on diode CR3, thusdisabling the crystal reference bank 34. Diode CR10 is also cut off.

Refer now to FIG. 6B. Transistors Q5 and 02 are cut off,

also, thus allowing the sweep to start.

When the selected channel is approached in frequency, the crystal in thechannel selector 12 being resonant at a frequency approximately 35I-IKz. lower in frequency than the corresponding crystal in the crystalreference bank 34 (the basic oscillator 24 heterodyned scanning signalscans from lower to higher frequencies), the channel selector 10 removesthe disable voltage and makes the next crystal in the missile crystalreference bank 34 the desired one. This represents a change from Mode 2to Mode 3.

b. Continuing again with Mode 2, and now referring back to FIG. 6A, the-12 V mode voltage is distributed through resistor R2, diodes CR 6 andCR 9, and, referring now to FIG. 6B, into the base of the p-n-ptransistor 07, which saturates its collector and disables the missilereceiver IF and RF loop frequency discriminator 66. CR 1 is a 3.3 VZener diode which holds the low potential end of condenser C10 to avalue of +2.7 volts, thus allowing it to charge up with the sweep.Conduction of transistor 07 shorts out the missile receiverdiscriminator 66 and prevents a false lock on spurious signals, as maybe seen from FIGS. 6A and 6B where they join.

The active and equivalent circuit for Mode 2 operation is shown in FIG.9.

Referring back to FIG. 6B, transistor O6 is switched on and transistor04 is switched on. When transistor O6 is switched on, resistor R14,approximately 8209, and resistor R13 are effectively connected inparallel (see FIG. 9B). This parallel combination of resistors changesthe sweep rate to approximately 60 msec. for a complete channel sweep.This sweep is unidirectional, upward in voltage and frequency. See FIG.3.

When the sweep has arrived at the proper frequency in the launcherchannel selector K0, the mode voltage goes from 1 2 V DC to zero at theend of Mode 2, as may be seen fom FIG. 2C. Capacitor C10 in FIG. 6Bprovides a long time constant downward in ramp voltage, which is thevaractor 25 voltage. The long time constant is made possible by currenttransformation in a transistor, base to emitter. Increasing DC betasresult in longer time constants.

c. Finally, and still referring to FIG. 6B, the 12-volt mode voltage isdistributed through diode CR 8, which is a 24 V Zener diode, throughresistor Rio and into the base of transistor 06 which is a p-n-pswitching transistor. It is this switch Q6 that changes the sweep from alOO-millisecond rate to one of several seconds. These are the rates andtimes involved in the sweep rising from volts to 15 volts. The fastsweep is related to Mode 2, and the slow sweep to Mode 3 as may be seenfrom FIG. 3.

Now with increasing time, within 1 msec. after the presetselect switch15 has been set to the select position 158 (see FIG. 53), as thefrequency of the basic oscillator 24 rises and its related lower IFfrequency is scanning upward in the launcher channel selector 10, itarrives at a crystal or other band-pass element with the desired channelfrequency. The signal is passed through (a window) which in turntriggers the -l 2-volt mode voltage off to zero voltage in 0.5millisecond or less.

Mode 2 requires 18 to 100 milliseconds to complete depending on thespecific channel; 18 milliseconds for channel 1 and bill!) millisecondsfor channel 19 in the embodiment actually built. s

Mode 3: Missile Launcher and Missile The switch from Mode 2 to Mode 3 isinitiated electronically by the launcher channel selector by a sweepscan frequency corresponding to a single crystal or band-pass frequencyin the crystal selector unit 12. The preset-select switch remains in itsselect or open position 1153. The Mode 3, zero mode, voltage isconsummated 0.5 sec. after Mode 2 is completed.

Disable voltages are removed from the crystal reference bank 34 and themissile receiver frequency discriminator 66, causing the crystalreference bank 3% and the missile discriminator as to become active (seeFIG. 1). Transistor Q6 (Fifi. 6B) is inactive, or cut off, and the slowsweep rate prevails (see Mode 3, in FIG. 3), and drifts upward into thecapture region R (see FIG. 2A) of the missile receivers discriminator66. If a reference signal, that is, a radar signal, is available in thereceiver loop 60, it will lock onto this loop.

Transistors Q6 and Q4 are cut off and as may 'be seen in FIG. 3, thelong time constant sweep results. See A, B, C, of FIG. 2 for theposition where this takes place. As presented in FIG. 2, the sweepcontinues on toward crystal 6 in the missile. If a signal is present inthe region of R in the receiver frequency discriminator 66, capture willbe made and the sweep stopped. it is the channel width allowing :2 MHz.radar error limits at the X band. The :2. MHZ. is divided in R region;the R bandwidth is 4 MHZ.

If no signal is present in the discriminator b6, the frequency sweepwill continue upward up to the resonant frequency of crystal No. 6, andthe sweep will stop there, indicating that the crystal reference (X-R)loop 20 is now in control. Effectively, the sweep frequency locks ontothe X-R loop. The X-R loop 2% forms a barricade or guard band in thedesired channel (see FlG. 2C}. When the missile receiver is active, itwill preempt control of the basic oscillator 2 as the guard bandprovides a standby position for capture by the missile receiver loop 60.When a receiver signal develops within the region of R, it will pull thebasic oscillator 24 lower in frequency to band center of the receiverfrequency discriminator as. The position at 6 is the stand by frequencywhich sets up the guard band limits. Fosition s is just an example, itcan be any one of 19 crystals in the embodiment shown.

The missile can now be launched.

TABLE OF COMPONENT VALUES FOR FIGS. 6A AND Obviously many modificationsand variations of the present invention are possible in the light of theabove teachings. It is therefore to be understood that within the scopeof the appended claims the invention may be practiced otherwise than asspecifically described.

Iclaim:

l. A multichannel frequency-select system wherein the frequency of acrystal in a crystal bank on a missile controls a voltage on avoltage-sensitive capacitor, such as a varactor, and is to be selectedto correspond with the frequency of a crystal in a crystal bank on achannel selector on a missile launcher, the frequency-select systembeing capable of operating at any of a plurality of crystal-controlledfrequencies in the missile, and in any one of three different modes:

1. a preset Mode 1, in which the intermediate frequency (IF) in both themissile launcher channel selector and the missile is a rest frequency,with a corresponding constant voltage on the varactor;

2. a select Mode 2, in which the frequency spectrum covered by thecrystal bank in the missile and the single crystal in the launcherchannel selector is swept or scanned at a ripid rate, with acorresponding voltage on the varactor rising at a greater rate; and

. an acquire Mode 3, wherein the scanning rate slows down and stops whenfrequency lock is acquired, with a cor responding voltage on thevaractor rising at a lesser rate, the three kinds of varactor voltages,the constant and the Z-speed ramp voltage, appearing first in circuitryon the missile;

the multichannel frequency-select system comprising:

a launcher channel selector on the missile launcher includa crystalchannel selector, which includes:

a plurality of crystals, or crystal bank, arranged in order ofincreasing resonant frequency; and

a multiposition switch, for choosing that one of the plurality ofcrystals at which the missile is to operate;

a mode logic circuit operatively connected to the crystal channelselector and including a preset-select switch which determines the modeof operation and furnishes proper mode direct-current voltages to themissile at a precise time;

a mode control circuit, located on themissile, having as an input thethree DC mode voltages from the mode logic circuit in the missilelauncher channel selector, which mode voltages trigger the one constantand two sweep voltages in the mode control circuit, which subsequentlyappear on the varactor;

a crystal-reference (X-R) loop on the missile including:

a basic frequency generator, whose frequency is controlled by thevoltage-sensitive capacitor in its tank circurt;

a crystal reference bank, having the same plurality of crystals as thecrystal channel. selector in the missile launcher, one of whose inputsis an output from the mode control circuit, and the other of whoseinputs is A an output from the basic frequency generator, which sweepsthe frequency spectrum of the crystals in the crystal reference bankuntil the frequency of the selected crystal is reached, at which timethe frequency sweeping in the crystal reference bank stops at thepredetermined crystal, whereupon the frequency sweeping in the launcherstops; an AC to DC converter, operatively connected to the crystalreference bank, for converting the radiofrequency from the crystal bankinto a direct current which supplies the lock and error signals for theX-R loop; an automatic frequency control (AFC) circuit having an inputfrom the mode control circuit and from the AC to DC converter, whichprovides the DC voltage in Mode l and the 2-speed ramp voltage for Mode2 and Mode 3 to the voltage-sensitive capacitor in the tank circuit ofthe basic frequency generator, -for increasing the frequency of thebasic frequency generator until operation at the selected frequency isachieved. 2. A multichannel frequency-select system according to claim1, wherein:

the basic frequency generator comprises:

a basic LC oscillator whose frequency is controlled by thevoltage-sensitive capacitor; and a buffer amplifier for amplifying theoutput of the basic oscillator. 3. A multichannel frequency-selectedsystem according to claim 2, wherein:

the X-R loop on the missile further comprises:

a transfer oscillator, operating at a fixed frequency; a transferoscillator, operating at a fixed frequency; an X-R mixing circuit havingas its two inputs outputs from the buffer amplifier and the transferoscillator, to produce a missile low intermediate frequency which variesdirectly as the voltage on the varactor; a missile channel-select lowintermediate frequency amplifier, for amplifying the IF;

the launcher channel selector on the missile launcher further comprises:

a launcher low IF amplifier and automatic gain control,

operatively connected to the missile channel-select low IF amplifier andhaving an output to the crystal channel selector, for amplifying the IFfrequency.

4. A multichannel; frequency-select system according to claim 3, furtherincluding:

a missile receiver loop which preempts control of the multichannelfrequency-select system when there is a signal at its input, the missilereceiver loop including the following components from the missilecrystal-reference (X-R) loop: the varactor; the AFCcircuit; the basicoscillator; the buffer amplifier; and wherein the basic frequencygenerator includes:

a frequency multiplier, whose input is the output of the bufferamplifier, for multiplying the frequency of the basic oscillator;

a radar state at the input to the missile receiver loop for interceptingand detecting a signal reflected off a target;

the missile receiver loop further comprising:

a missile receiver mixing state for mixing the output of the frequencymultiplier with the output of the radar stage; a missile receiver IFamplifier for amplifying the output of the missile receiver mixingstate; a frequency discriminator, for providing lock and error signalsto the AFC circuit in the missile receiver loop; the relationshipof thefrequency discriminator output to the other inputs to the AFC circuitbeing such that when a target signal is present in the missile receiver,which corresponds to an active missile receiver loop, the frequencydiscriminator preempts control of the basic oscillator, while if theradar signal IS interrupted or lost, the circuits associated with theX-R AFC circuit, the 'X-R loop, resume control until the missilereceiver loop is active again.

1. A multichannel frequency-select system wherein the frequency of acrystal in a crystal bank on a missile controls a voltage on avoltage-sensitive capacitor, such as a varactor, and is to be selectedto correspond with the frequency of a crystal in a crystal bank on achannel selector on a missile launcher, the frequency-select systembeing capable of operating at any of a plurality of crystal-controlledfrequencies in the missile, and in any one of three different modes: 1.a preset Mode 1, in which the intermediate frequency (IF) in both themissile launcher channel selector and the missile is a rest frequency,with a corresponding constant voltage on the varactor;
 2. a select Mode2, in which the frequency spectrum covered by the crystal bank in themissile and the single crystal in the launcher channel selector is sweptor scanned at a ripid rate, with a corresponding voltage on the varactorrising at a greater rate; and
 3. an acquire Mode 3, wherein the scanningrate slows down and stops when frequency lock is acquired, with acorresponding voltage on the varactor rising at a lesser rate, the threekinds of varactor voltages, the constant and the 2-speed ramp voltage,appearing first in circuitry on the missile; the multichannelfrequency-select system comprising: a launcher channel selector on themissile launcher including: a crystal channel selector, which includes:a plurality of crystals, or crystal bank, arranged in order ofincreasing resonant frequency; and a multiposition switch, for choosingthat one of the plurality of crystals at which the missile is tooperate; a mode logic circuit operatively connected to the crystalchannel selector and including a preset-select switch which determinesthe mode of operation and furnishes proper mode direct-current voltagesto the missile at a precise time; a mode control circuit, located on themissile, having as an input the three DC mode voltages from the modelogic circuit in the missile launcher channel selector, which modevoltages trigger the one constant and two sweep voltages in the modecontrol circuit, which subsequently appear on the varactor; acrystal-reference (X-R) loop on the missile including: a basic frequencygenerator, whose frequency is controlled by the voltage-sensitivecapacitor in its tank circuit; a crystal reference bank, having the sameplurality of crystals as the crystal channel selector in the missilelauncher, one of whose inputs is an output from the mode controlcircuit, and the other of whose inputs is an output from the basicfrequency generator, which sweeps the frequency spectrum of the crystalsin thE crystal reference bank until the frequency of the selectedcrystal is reached, at which time the frequency sweeping in the crystalreference bank stops at the predetermined crystal, whereupon thefrequency sweeping in the launcher stops; an AC to DC converter,operatively connected to the crystal reference bank, for converting theradiofrequency from the crystal bank into a direct current whichsupplies the lock and error signals for the X-R loop; an automaticfrequency control (AFC) circuit having an input from the mode controlcircuit and from the AC to DC converter, which provides the DC voltagein Mode 1 and the 2-speed ramp voltage for Mode 2 and Mode 3 to thevoltage-sensitive capacitor in the tank circuit of the basic frequencygenerator, for increasing the frequency of the basic frequency generatoruntil operation at the selected frequency is achieved.
 2. A multichannelfrequency-select system according to claim 1, wherein: the basicfrequency generator comprises: a basic LC oscillator whose frequency iscontrolled by the voltage-sensitive capacitor; and a buffer amplifierfor amplifying the output of the basic oscillator.
 2. a select Mode 2,in which the frequency spectrum covered by the crystal bank in themissile and the single crystal in the launcher channel selector is sweptor scanned at a ripid rate, with a corresponding voltage on the varactorrising at a greater rate; and
 3. A multichannel frequency-selectedsystem according to claim 2, wherein: the X-R loop on the missilefurther comprises: a transfer oscillator, operating at a fixedfrequency; a transfer oscillator, operating at a fixed frequency; an X-Rmixing circuit having as its two inputs outputs from the bufferamplifier and the transfer oscillator, to produce a missile lowintermediate frequency which varies directly as the voltage on thevaractor; a missile channel-select low intermediate frequency amplifier,for amplifying the IF; the launcher channel selector on the missilelauncher further comprises: a launcher low IF amplifier and automaticgain control, operatively connected to the missile channel-select low IFamplifier and having an output to the crystal channel selector, foramplifying the IF frequency.
 3. an acquire Mode 3, wherein the scanningrate slows down and stops when frequency lock is acquired, with acorresponding voltage on the varactor rising at a lesser rate, the threekinds of varactor voltages, the constant and the 2-speed ramp voltage,appearing first in circuitry on the missile; the multichannelfrequency-select system comprising: a launcher channel selector on themissile launcher including: a crystal channel selector, which includes:a plurality of crystals, or crystal bank, arranged in order ofincreasing resonant frequency; and a multiposition switch, for choosingthat one of the plurality of crystals at which the missile is tooperate; a mode logic circuit operatively connected to the crystalchannel selector and including a preset-select switch which determinesthe mode of operation and furnishes proper mode direct-current voltagesto the missile at a precise time; a mode control circuit, located on themissile, having as an input the three DC mode voltages from the modelogic circuit in the missile launcher channel selector, which modevoltages trigger the one constant and two sweep voltages in the modecontrol circuit, which subsequently appear on the varactor; acrystal-reference (X-R) loop on the missile including: a basic frequencygenerator, whose frequency is controlled by the voltage-sensitivecapacitor in its tank circuit; a crystal reference bank, having the sameplurality of crystals as the crystal channel selector in the missilelauncher, one of whose inputs is an output from the mode controlcircuit, and the other of whose inputs is an output from the basicfrequency generator, which sweeps the frequency spectrum of the crystalsin thE crystal reference bank until the frequency of the selectedcrystal is reached, at which time the frequency sweeping in the crystalreference bank stops at the predetermined crystal, whereupon thefrequency sweeping in the launcher stops; an AC to DC converter,operatively connected to the crystal reference bank, for converting theradiofrequency from the crystal bank into a direct current whichsupplies the lock and error signals for the X-R loop; an automaticfrequency control (AFC) circuit having an input from the mode controlcircuit and from the AC to DC converter, which provides the DC voltagein Mode 1 and the 2-speed ramp voltage for Mode 2 and Mode 3 to thevoltage-sensitive capacitor in the tank circuit of the basic frequencygenerator, for increasing the frequency of the basic frequency generatoruntil operation at the selected frequency is achieved.
 4. A multichannelfrequency-select system according to claim 3, further including: amissile receiver loop which preempts control of the multichannelfrequency-select system when there is a signal at its input, the missilereceiver loop including the following components from the missilecrystal-reference (X-R) loop: the varactor; the AFC circuit; the basicoscillator; the buffer amplifier; and wherein the basic frequencygenerator includes: a frequency multiplier, whose input is the output ofthe buffer amplifier, for multiplying the frequency of the basicoscillator; a radar state at the input to the missile receiver loop forintercepting and detecting a signal reflected off a target; the missilereceiver loop further comprising: a missile receiver mixing state formixing the output of the frequency multiplier with the output of theradar stage; a missile receiver IF amplifier for amplifying the outputof the missile receiver mixing state; a frequency discriminator, forproviding lock and error signals to the AFC circuit in the missilereceiver loop; the relationship of the frequency discriminator output tothe other inputs to the AFC circuit being such that when a target signalis present in the missile receiver, which corresponds to an activemissile receiver loop, the frequency discriminator preempts control ofthe basic oscillator, while if the radar signal is interrupted or lost,the circuits associated with the X-R AFC circuit, the X-R loop, resumecontrol until the missile receiver loop is active again.
 10. Refer toFIG. 5B. The preset switch 15 is still open. Transistor Q-C (2N2907A)cuts off, the +19.0 V DC voltage at resistor R2 drops out. TransistorQ-B (2N2222A) conducts, the -19.0 V DC cuts in. Transistor Q-A (2N894),which is a switching transistor, remains cut off. Mode signal voltage onmode signal line 18 is now -19.0 V DC as a result of transistor Q-Bconducting. Meanwhile the basic oscillator 24 in the missile starts upfrom its rest frequency of approXimately 4.0 MHz. (see FIG. 3) andsweeps upward in frequency. When the RF frequency reaches the band-passor crystal frequency, it fires the transistor Q-A (2N894), asilicon-controlled rectifier, which immediately decreases the magnitudeof the mode voltage from -12 V DC to zero, at the end of Mode 2, in 0.5msec. or less. See FIG. 2C. As may be seen in FIG. 8, the crystal Y-Nprovides the path between the low IF amplifier 16 and the Q-A SCR. TheSCR fires on RF signal, its action being not unlike that of a thyratron.In the laboratory embodiment, and referring back to FIG. 5B, if theoperator wishes to select a different channel before missile launch, thepreset-select switch 15 is returned from the select position 15B to thepreset position 15A, the desired channel is switched in, then the switch15 is returned from the preset position 15A to the select position 15B.There is no limit on the number of times this can be done except forconsiderations of battery life of the missile. While the battery life isapproximately 12 min. in the embodiment actually built, only 0.5 min. ofthis represents the drain on the missile launcher. Mode 2: Missile Thefollowing is what transpires in the missile in Mode
 2. As stated above,within 1 msec. after the preset-select switch 15 is flipped to theselect position 15B (see FIG. 5B), the mode voltage changes from +12.0to -120 V (see FIG. 2C). Within this same time of 1 msec., the -12 Vmode voltage is distributed as follows, referring first to FIG. 6A. a.through the two resistors R11 and R20 forming a voltage divider. Thisnegative voltage of 12 V puts a reverse bias on diode CR3, thusdisabling the crystal reference bank
 34. Diode CR10 is also cut off.Refer now to FIG. 6B. Transistors Q5 and Q2 are cut off, also, thusallowing the sweep to start. When the selected channel is approached infrequency, the crystal in the channel selector 12 being resonant at afrequency approximately 35 HKz. lower in frequency than thecorresponding crystal in the crystal reference bank 34 (the basicoscillator 24 heterodyned scanning signal scans from lower to higherfrequencies), the channel selector 10 removes the disable voltage andmakes the next crystal in the missile crystal reference bank 34 thedesired one. This represents a change from Mode 2 to Mode
 3. b.Continuing again with Mode 2, and now referring back to FIG. 6A, the -12V mode voltage is distributed through resistor R2, diodes CR 6 and CR 9,and, referring now to FIG. 6B, into the base of the p-n-p transistor Q7,which saturates its collector and disables the missile receiver IF andRF loop frequency discriminator
 66. CR 1 is a 3.3 V Zener diode whichholds the low potential end of condenser C10 to a value of +2.7 volts,thus allowing it to charge up with the sweep. Conduction of transistorQ7 shorts out the missile receiver discriminator 66 and prevents a falselock on spurious signals, as may be seen from FIGS. 6A and 6B where theyjoin. The active and equivalent circuit for Mode 2 operation is shown inFIG.
 9. Referring back to FIG. 6B, transistor Q6 is switched on andtransistor Q4 is switched on. When transistor Q6 is switched on,resistor R14, approximately 820 Omega , and resistor R13 are effectivelyconnected in parallel (see FIG. 9B). This parallel combination ofresistors changes the sweep rate to approximately 60 msec. for acomplete channel sweep. This sweep is unidirectional, upward in voltageand frequency. See FIG.
 3. When the sweep has arrived at the properfrequency in the launcher channel selector 10, the mode voltage goesfrom -12 V DC to zero at the end of Mode 2, as may be seen fom FIG. 2C.Capacitor C10 in FIG. 6B provides a long time constant downward in rampvoltage, which is the varactor 25 voltage. The long time constant ismade possible by current transformation in a transistor, base toemitter. Increasing DC betas result in longer time constants. c.Finally, and still referring to FIG. 6B, the -12-volt mode voltage isdistributed through diode CR 8, which is a 24 V Zener diode, throughresistor R16 and into the base of transistor Q6 which is a p-n-pswitching transistor. It is this switch Q6 that changes the sweep from a100-millisecond rate to one of several seconds. These are the rates andtimes involved in the sweep rising from 0 volts to 15 volts. The fastsweep is related to Mode 2, and the slow sweep to Mode 3 as may be seenfrom FIG.
 3. Now with increasing time, within 1 msec. after thepreset-select switch 15 has been set to the select position 15B (seeFIG. 5B), as the frequency of the basic oscillator 24 rises and itsrelated lower IF frequency is scanning upward in the launcher channelselector 10, it arrives at a crystal or other band-pass element with thedesired channel frequency. The signal is passed through (a window) whichin turn triggers the -12-volt mode voltage off to zero voltage in 0.5millisecond or less. Mode 2 requires 18 to 100 milliseconds to completedepending on the specific channel; 18 milliseconds for channel 1 andb100 milliseconds for channel 19 in the embodiment actually built. Mode3: Missile Launcher and Missile The switch from Mode 2 to Mode 3 isinitiated electronically by the launcher channel selector 10 by a sweepscan frequency corresponding to a single crystal or band-pass frequencyin the crystal selector unit
 12. The preset-select switch 15 remains inits select or open position 15B. The Mode 3, zero mode, voltage isconsummated 0.5 sec. after Mode 2 is completed. Disable voltages areremoved from the crystal reference bank 34 and the missile receiverfrequency discriminator 66, causing the crystal reference bank 34 andthe missile discriminator 66 to become active (see FIG. 1). TransistorQ6 (FIG. 6B) is inactive, or cut off, and the slow sweep rate prevails(see Mode 3, in FIG. 3), and drifts upward into the capture region R(see FIG. 2A) of the missile receiver''s discriminator
 66. If areference signal, that is, a radar signal, is available in the receiverloop 60, it will lock onto this loop. Transistors Q6 and Q4 are cut offand as may be seen in FIG. 3, the long time constant sweep results. SeeA, B, C, of FIG. 2 for the position where this takes place. As presentedin FIG. 2, the sweep continues on toward crystal 6 in the missile. If asignal is present in the region of R in the receiver frequencydiscriminator 66, capture will be made and the sweep stopped. R is thechannel width allowing + or - 2 MHz. radar error limits at the X band.The + or -
 2. MHz. is divided in R region; the R bandwidth is 4 MHz. Ifno signal is present in the discriminator 66, the frequency sweep willcontinue upward up to the resonant frequency of crystal No. 6, and thesweep will stop there, indicating that the crystal reference (X-R) loop20 is now in control. Effectively, the sweep frequency locks onto theX-R loop. The X-R loop 20 forms a barricade or guard band in the desiredchannel (see FIG. 2C). When the missile receiver is active, it willpreempt control of the basic oscillator 24 as the guard band provides astandby position for capture by the missile receiver loop
 60. When areceiver signal develops within the region of R, it will pull the basicoscillator 24 lower in frequency to band center of the receiverfrequency discriminator
 66. The position at 6 is the stand by frequencywhich sets up the guard band limits. Position 6 is just an example, itCan be any one of